In the field of wireless communications, wireless mobile communication devices (“mobile devices”) such as cellular phones, and personal digital assistants with integrated wireless communications, move from regions of service to regions without service. Additionally, mobile devices can be initialized in areas either with or without service. When a mobile device does not have service, it performs a signal acquisition scan to determine if there is a usable signal available. This acquisition scan typically scans the channels defined in a predetermined frequency band to determine which of the channels contain a signal that can be used to obtain service.
The plurality of channels defined in a frequency band are used to permit a plurality of service providers to offer cellular service. Typically, a frequency band is divided into 255 channels. Each service provider is typically allocated a number of channels in each frequency band so that it can situate a number of cellular service sites to create a series of overlapping coverage areas. Each cellular service site typically provides encoded signals on a number of distinct channels to allow for technologies such as frequency hopping.
Many mobile devices are compliant with the standards established through the Global System for Mobile Communications (GSM). In compliance with the GSM standard, conventional mobile devices sequentially scan all the channels in the allocated frequency band to create a list of the channels that contain GSM encoded signals. The channel with the highest signal power in the list that allows the mobile device to register with its associated network is used to provide the mobile device network connectivity. If there are no networks that offer the mobile device registration, the mobile device selects the channel with the highest signal power and registers for emergency service on the corresponding network. This network selection process is governed by a number of GSM standards, including GSM standard 5.08.
When a mobile device does not detect a channel with which it can register, it periodically rescans the channels to determine if service has become available. When a mobile device is in a region that does not offer service it typically consumes significant power, as the scanning process is a power intensive operation. Thus, a mobile device in a region without service will consume a great deal of power unless the time between scans is large in relation to the amount of time that the scan takes. Although increasing the time between scans increases battery life, it decreases the possibility that the user of the mobile device will be able obtain service as soon as it becomes available. Thus, designers of signal acquisition methods must design a tradeoff between battery power conservation and signal acquisition times.
It would, therefore, be advantageous for a mobile device to be able to offer both rapid discovery of available GSM channels and improved battery life while performing these channel scans.